Comparison and analysis of drainage measures for draining accumulated water condensed from wet CBM and transported in surface gathering pipeline network

When compared with conventional gas field development, the coalbed methane (CBM) production process has its unique features that the produced natural gas contains saturated vapor and the gathering system is characterized as two-phase flow and liquid drainage. This paper aims to compare the drainage measures for draining liquid that condenses from wet CBM and transported in surficial gathering pipeline network. The unsteady non-fully developed flow of wet CBM in dendritic gathering and transmission pipeline network was simulated and analyzed. Phase change of water vapor was presented during the low-liquid loading flow and heat transfer process. The mass flow rate in pipeline network was supposed to increase continuously due to the aggregation and accumulation of liquid. The pressure at some adjacent nodes was validated by experimental data in situ. Three measurements for draining liquid are proposed, which include pigging, installing devices and cooling fluid at pipe inlet. It is concluded that the optimal strategy is combining the pigging method with installing several drainage devices rather than only pigging or the combination of pigging and cooling. Additionally, the presented model is a worthy way to optimize the pigging cycle to ensure the high efficient operation for the pipeline. Therefore, this paper provides a safe and economic method for the flow assurance of wet CBM fields.